When operating a motor vehicle, such as an automobile, light-duty truck, heavy duty truck, tractor-trailer, and the like, it may not be possible to visually detect objects that lie within the path of the motor vehicle. This is particularly true when backing the motor-vehicle because blind spots and/or non-optimal lines of sight may dictate reliance on mirrors to view the path into which the motor vehicle is being moved. However, backing is not the only time when an object may not be within the view of the operator. Objects, and particularly objects very near either the front or rear of the vehicle, may be difficult to visually detect from the normal operating position of the motor vehicle.
To aid motor vehicle operators in detecting objects that may lie in the path of the motor vehicle, object detection systems have been proposed and implemented on some motor vehicles. These object detection systems, typically using ultra-sonic energy, include one or more sensors fitted to a bumper of the motor vehicle. Each sensor includes a transmitter capable of illuminating a field in which the objects are to be detected with an energy emission. The sensor also includes a receiver that listens for an energy return. If an object is located within the field, a portion of the energy emission will be reflected from the object and detected by the receiver. In this event, the system will typically also include an alert, audio or visual or both, to alert the vehicle operator as to the presence of the object within the field.
The above systems are generally intended to operate while the motor vehicle is moving. To provide as much reaction time as possible to the operator, it is desirable to detect an object coming within the path of the motor vehicle at as great a distance from the vehicle as possible. At the same time, it is possible an object may come into the path of the vehicle at a position that is closely adjacent to the vehicle. These objects must also be detected. Detection of objects located far from the vehicle will typically require use of more sensing energy than the detection of objects that are located near to the vehicle. However, at energy levels that are high enough to detect a remote object, significant noise can appear that may interfere with detection of near objects or even with detection of the remote object. Noise can be the result of the sensing energy deflecting from the ground, from laterally located objects not in the vehicle path or from multipath sources. Noise may also be introduced from external sources. The noise can cause return signals that are wrongly interpreted as objects or may mask the energy returns of actual objects.
Some detection systems, such as those that utilize ultrasonic energy as the sensing energy, may use one or more transceivers that both generate the sensing energy and detect energy returns from the detection field. Such devices advantageously utilize the same transducer element as a transmitter and as a receiver and are thus low cost. Transceiver based systems can suffer from poor object detection; particularly when the object is near to the vehicle. Once the transceiver is energized to send sensing energy into the detection field, there is a period that extends longer than the actual time the transceiver is energized during which it is not capable of detecting energy returns. The transducer element within the transceiver continues to oscillate "ring" during this period much like a bell rings after being struck. This period is referred to as the "ringout" period. An object may be close enough to the transceiver that energy returns from the object may fall within the ringout period and may thus be undetectable.
Thus, there is a need for an improved object detection system that is robust in both near object and far object detection.